Driers for divided material



Jan. 4, 1966 A. MARK 3,226,841

DRIERS FOR DIVIDED MATERIAL Filed March 20, 1962 N. B a5 b H 4 4 r 5 N .ci

United States Patent 3,226,841 DRIERS FOR DIVIDED MATERIAL Andr Mark, 54, Cours Lafayette, Lyon, France Filed Mar. 20, 1962, Ser. No. 181,114 Claims priority, application France, Mar. 27, 1961, 41,390, Patent 1,293,023 2 Claims. (CI. 3457) This invention relates to driers for divided material of the kind in which the material to be dried is fluidized on a gas-permeable supporting wall by an ascending draft of drying gas. a

In such driers the gas-permeable Wall which supports the material to be dried may be in the form of a perforated metallic plate, but such plates do not ensure a quite uniform distribution of the gas and in some zones the moist material sticks to the plate between the perforations. This disadvantage may be avoided with supporting walls made of a porous substance, but such plates create high head losses which entail an abnormal power consumption. It should further be noted that in such driers the drying gas passes through the layer of material tobe dried at a relatively high velocity. Since the thickness of the layer is limited on account of the resistance which a too thick layer would oppose to the gas flow, the gas which issues from the upper side of the said layer is still relatively hot and dry, i.e. the drying power of the gas supplied to the dryer is only very poorly used. This inconvenience may be avoided by recycling a large proportion of the gas' issuing from the drier, but this gas contains a substantial amount of fine dust from the dried material and in the case of supporting'walls in the form of porous plates the pores are rapidly clogged, unless the recycled gas is filtered, which necessitates an expensive auxiliary equipment and substantially increases the power required.

The present invention has for its object to avoid these drawbacks. 1

In accordance with the present invention in a drier of kind set forth, the gas-permeable Wall is formed of a layer of ball-like members comprised between two superposed perforated partitions.

In the annexed drawings:

FIG. 1 is a general view with parts in section, showing a drier according to the present invention.

FIG. 2 is a cross-section illustrating a constructional embodiment of the drier.

FIG. 3 is a diagra-mmatical cross-section of a layer formed of balls of different diameters.

The drier illustrated comprises a main casing 1 of rectangular horizontal section the bottom 1a of which is inclined downwardly towards the outlet of a conduit 2 connected with the exhaust of a blower 3. The inlet 4 of blower 3 is connected by a conduit 5 with an air heater 6 and by another conduit 7 with the cover 1b of casing 1. From this conduit 7 extends a third conduit 8 which opens tangentially into a centrifugal separator or cyclone 9, the outlet of the latter being connected with the inlet of an exhaust blower 10.

Within casing 1 are disposed two spaced horizontal perforated partitions 11 and 12, the space comprised between these partitions being filled with balls 13 which may be charged through a valve 14 at one end of easing 1 and withdrawn through another valve 15 at the other end thereof. The material to be dried is introduced into casing 1 by means of a hopper 16 provided with a rotating air lock 17, through a chute 18 which opens above one end of the upper perforated partition 11 on which it forms a fluidized layer 19, as explained below. At the other end of partition 11 there is provided an exhaust chamberwith a rotating air lock 20 for passage of the dried material.

3,226,841 Patented Jan. 4, 1966 Casing 1 further comprises an upper horizontal tube 21 provided with spray heads 22 by means of which an appropriate liquid such as water may be sprayed in the apparatus as this will be explained below.

In the constructive embodiment illustrated in FIG. 2 casing 1 may be made in two parts, namely a downwardly opening upper part, which has been referenced 23 in FIG. 2, and an upwardly opening lower part referenced 24. The lower edge of part 23 has an outer flange 23a and the upper edge of part 24 has similarly an outer flange 24a. Partition '11 may be in the form of a wire gauze on which the treated material cannot stick, while partition 12 may be either another wire gauze or a per forated metal sheet. The edges of partitions 11 and 12 are reinforced by corresponding frames, respectively 25 and 26, made of sheet metal strips folded in U-shape on the edges of the partitions, the latter being maintained at the proper distance apart by distance members such as 27 through which are passed bolts 28 which assemble parts 23 and 24 together with partitions 11 and 12, and with members 26 themselves.

The operation of the drier illustrated is as follows:

Hot air from heater 6 is forced by blower 3 into the lower part of casing 1 (part 24 in the embodiment of FIG. 2). This air passes through the lower perforated partition 12, through the mass of balls 13, through the upper partition 11 andthence through the layer 19 of material to be dried, the ascending velocity of the air draft being such that the said layer is fluidized and flows therefore regularly from the outlet of chute 18 into which fresh material is continuously fed by hopper 16 and air lock 17, to the exhaust chamber at the left-hand end of easing 1, from which or it continuously exhausts through air-lock 20. The air issuing from layer 19, i.e. from the material under treatment, reaches the cover 1b of casing 1. A determined percentage of this air is drawn by the exhaust blower 10 through cyclone 9 and is rejected into the atmosphere, while the bulk returns to blower 3 through conduit 7 to be recycled into the drier.

The air which passes upwardly through the layer formed by balls 13 also fluidizes this layer or at least causes the balls to move at random and to strike against each other. This continuous vibration of the mass of balls ensures a quite uniform distribution of the drying air and prevents any clogging by the fine dust in suspension in the air recycled from the upper part of casing 1. This dust passes through the vibrating screen formed by balls 13 and is mostly superficially retained by the still moist material fluidized on partition 11.

If the balls have nevertheless retained some particles of the material carried by the recycled air, they may be readily washed in situ. For this purpose the drier is operated without any material to be dried and water (or any appropriate liquid) is sprayed on partition 11 by means of tube 21. The balls are thus effectively washed, the liquid with dust particles in suspension being evacuated, as for instance by a lower syphon tube such as 29.

When it is desired to change the balls, valves 14 and 15 are opened while the main blower is operated at full rate, the apparatus of course containing no material. The layer formed by balls 13 is therefore fluidized and flows through valve 15 as a liquid, while fresh balls are con t-inuously introduced through valve 15 in order to maintain a continuous layer on partition 12. When all the balls have thus been changed valves 14 and 15 may again be closed.

It will be noted that the air recycled into the drier does not pass through a filter or dust separator. Cyclone 9 only deals with the spent drying air which is rejected into the atmosphere and which only represents a fraction of the air flow issuing from the drier.

Balls 13 may be of any appropriate substance, as for instance glass, ceramic material, metal, etc. Their diameter is selected in accordance with their specific weight and with the ascending velocity of the drying air.

It may be of advantage to provide balls of different diameters, as shown in FIG. 3 wherein the layer comprises balls 13a of relatively large diameter which are more or less unaffected by the ascending air draft and therefore constitute a lower layer acting for uniformly distributing the drying air, and balls 13b of relatively small diameter which are fluidized and form a vibrating porous layer against the upper partition 11.

Instead of balls proper there could be used an appropriate calibrated material such as for instance silica.

It will be appreciated that the upper partition 11 may be slightly inclined downwardly from its feed end to its outlet end. The lower partition 12 may also be inclined in the same direction.

In a practical run the drier described was used for drying a product formed of particles of 40 to 100 i.e. quite fine and clogging. The balls used were of glass, with a diameter of 1.75 mm., and they formed between partitions 11 and 12 a layer of about 45 mm. in thickness. The head losses through the balls amounted to about 20 mm. (water gauge) and remained substantially constant during the whole run. The ascending velocity of the air draft was about 16 metres per minute.

After seven hours the drier was stopped and the balls were examined. They were found quite clean apart from some traces of ultrafine dust which could easily be eliminated by means of the water spray.

The balls were further observed through the upper partition 11, the apparatus being operated without any material under treatment. It could thus be ascertained that the balls were vibrating and that they continuously rotated on themselves.

In another example in the drying of granulated fertilizers with a particle dimension between 1 and 4 mm., the air velocity was about 60 metres per minute, the

thickness of the layer of balls was about 20 mm. and the head losses through this layer amounted to mm., which is a relatively small value for a relatively high air veloc1ty.

I claim:

1. A drier for divided material comprising an upper substantially horizontal perforated partition to support the divided material to be dried in the form of a gaspermeable fluidized bed; a second substantially horizontal perforated partition disposed under said upper partition and defining therewith an intermediate chamber; balllike members in said intermediate chamber to form therein a fiuidizable gas permeable layer; and means to force a drying gas through said lower partition to cause said gas to flow vertically through said layer of ball-like members, through said upper partition and through said bed of material to be dried so as to fiuidize said bed and at least the upper portion of said layer to cause said ball-like members to strike against said upper partition to prevent said material from adhering thereto.

2. In an apparatus as claimed in claim 1, said intermediate chamber having a first end and a second end, said first end being formed with a lower lateral outlet to discharge said layer of ball-like members in the fluidized state and said second end being formed with an upper lateral inlet for introduction of ball-like members to constitute said layer.

References Cited by the Examiner UNITED STATES PATENTS 2,529,366 11/1950 Bauer 263-53 2,565,179 8/1951 Lavalee 118-300 X 2,635,684 4/1953 Joscelyne.

2,654,659 10/ 1953 Friedman 23288 2,755,749 7/ 1956 Seymour.

2,760,917 8/1956 Ward 23-288 X 2,779,714 1/ 1957 Keith -104 X 2,852,545 9/1958 Jenny 165104 X 3,041,212 6/1962 Booth 134111 X 3,060,589 10/1962 Wallin 34-13 WILLIAM F. ODEA, Primary Examiner.

NORMAN YUDKOFF, Examiner.

I. SOFER, C. R. REMKE, Assistant Examiners. 

1. A DRIER FOR DIVIDED MATERIAL COMPRISING AN UPPER SUBSTANTIALLY HORIZONTAL PERFORATED PARTITION TO SUPPORT THE DIVIDED MATERIAL TO BE DRIED IN THE FORM OF A GASPERMEABLE FLUIDIZED BED; A SECOND SUBSTANTIALLY HORIZONTAL PERFORATED PARTITION DISPOSED UNDER SAID UPPER PARTITION AND DEFINING THEREWITH AN INTERMEDIATE CHAMBER, BALLLIKE MEMBERS IN SAID INTERMEDIATE CHAMBER TO FORM THEREIN A FLUIDIZABLE GAS PERMEABLE LAYER; AND MEANS TO FORCE A DRYING GAS THROUGH SAID LOWER PARTITION TO CAUSE SAID GAS TO FLOW VERTICALLY THROUGH SAID LAYER OF BALL-LIKE MEMBERS, THROUGH SAID UPPER PARTITION AND THROUGH SAID BED OF MATERIAL TO BE DRIED SO AS TO FLUIDIZE SAID BED AND AT LEAST 